1. Field of the Invention
The present invention relates generally to an iron-base sintered alloy used as a material for mechanical parts, and more particularly to an iron-base sintered alloy which exhibits excellent wear resistance and concordance with a contacting member in case of being used as the material for slidingly contacting sections of, for example, rocker arms and tappets of a valve operating mechanism of an internal combustion engine.
2. Description of the Prior Art
In recent years, wear of the parts of a valve operating mechanism of an internal combustion engine has become an issue with the requirement of increasing engine speed and engine output power, in which high durability of rocker arm and tappet at their slidingly contacting part to which a camshaft slidingly contacts has been particularly required. The slidingly contacting part of rocker arm and tappet is usually subjected to a high bearing pressure and therefore is required to have excellent wear resistance, scuffing resistance, pitting resistance, and concordance with the material of the camshaft.
In this regard, a rocker arm has hitherto been used, for example, the type made of chilled cast iron, the type wherein surface treatment such as Cr-plating and padding of self-fluxing or autogenous alloy upon thermal spraying is made, and the type formed of liquid phase sintered of compressed body of Fe-Cr-C high alloy powder.
However, of these types the rocker arm made of chilled cast iron is problematical because of being lower in pitting resistance and wear resistance. The Cr-plated rocker arm is problematical because of a peeling tendency of the plated layer. The rocker arm provided with the thermal spray padding is problematical because of scuffing and providing wear to a camshaft as an opposite member, and the like. The rocker arm formed of Fe-Cr-C sintered alloy usually exhibits considerably good characteristics as compared with the above-mentioned rocker arms; however, not only is its wear resistance insufficient but also the abrasion amount of the camshaft increases in case where high bearing pressure is applied to the rocker arm and the camshaft, thus failing to satisfy required characteristics for the material of mechanical parts of valve operating mechanism.